Resist composition and patterning process

ABSTRACT

A resist composition comprising an iodized base polymer and an iodized benzene ring-containing quencher has a high sensitivity and improved LWR and CDU.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2018-236571 filed in Japan on Dec. 18,2018, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a resist composition and a patterning processusing the composition.

BACKGROUND ART

To meet the demand for higher integration density and operating speed ofLSIs, the effort to reduce the pattern rule is in rapid progress. Thelogic devices used in smart phones or the like drive forward theminiaturization technology. Logic devices of 10-nm node are manufacturedin a large scale using a multi-patterning lithography process based onArF lithography.

In the application of lithography to next 7-nm or 5-nm node devices, theincreased expense and overlay accuracy of multi-patterning lithographybecome tangible. The advent of EUV lithography capable of reducing thenumber of exposures is desired.

Since the wavelength (13.5 nm) of extreme ultraviolet (EUV) is shorterthan 1/10 of the wavelength (193 nm) of ArF excimer laser, the EUVlithography achieves a high light contrast, from which a high resolutionis expectable. Because of the short wavelength and high energy densityof EUV, an acid generator is sensitive to a small dose of photons. It isbelieved that the number of photons available with EUV exposure is 1/14of that of ArF exposure. In the EUV lithography, the phenomenon that theedge roughness (LWR) of line patterns or the critical dimensionuniformity (CDU) of hole patterns is degraded by a variation of photonnumber is considered a problem.

Aiming to reduce a photon number variation, an attempt was made torender the resist more absorptive so that the number of photons absorbedin the resist is increased.

Patent Document 1 discloses a halogen-substituted styrene base resin.Among the halogen atoms, iodine is highly absorptive to EUV radiation ofwavelength 13.5 nm. Recently Patent Documents 2 to 4 propose to useiodine-substituted resins as EUV resist material. Regrettably, it is nottrue that a higher sensitivity is obtainable merely by incorporatingiodine to increase the number of photons absorbed. With respect to theacid generation in EUV exposure, Non-Patent Document 1 reports that theacid generation efficiency of iodized styrene is only 14% of that ofhydroxystyrene.

The EUV lithography resist must meet high sensitivity, high resolutionand low LWR at the same time. As the acid diffusion distance is reduced,LWR is reduced, but sensitivity becomes lower. For example, as the PEBtemperature is lowered, the outcome is a reduced LWR, but a lowersensitivity. As the amount of quencher added is increased, the outcomeis a reduced LWR, but a lower sensitivity. It is necessary to overcomethe tradeoff relation between sensitivity and LWR. It would be desirableto have a resist material having a high sensitivity and resolution aswell as improved LWR and CDU.

Patent Document 5 proposes a quencher of iodonium carboxylate typehaving a carboxylate ion bonded to an iodonium cation. Patent Documents6 and 7 propose the use of hypervalent iodine compounds as the quencher.Patent Document 8 discloses a sulfonium salt of iodized benzoic acid.Since iodine has a large atomic weight, quenchers in the form of iodizedcompounds are fully effective for suppressing acid diffusion.

CITATION LIST

-   Patent Document 1: JP-A H05-204157-   Patent Document 2: JP-A 2015-161823-   Patent Document 3: WO 2013/024777-   Patent Document 4: JP-A 2018-004812-   Patent Document 5: JP 5852490 (U.S. Pat. No. 9,176,379)-   Patent Document 6: JP-A 2015-180928 (U.S. Pat. No. 9,563,123)-   Patent Document 7: JP-A 2015-172746 (U.S. Pat. No. 9,448,475)-   Patent Document 8: JP-A 2017-219836-   Non-Patent Document 1: Jpn. J. Appl. Physics, Vol. 46, No. 7, pp.    L142-L144, 2007

SUMMARY OF INVENTION

For the acid-catalyzed chemically amplified resist, it is desired todevelop a resist composition providing a high sensitivity and reducingLWR or improving CDU of hole patterns.

An object of the invention is to provide a resist composition whichexhibits a high sensitivity, low LWR and improved CDU independent ofwhether it is of positive tone or negative tone, and a pattern formingprocess using the same.

The inventors have found that a resist composition comprising an iodizedpolymer and a quencher selected from a sulfonium or ammonium salt ofiodized benzene ring-containing carboxylic acid, a sulfonium or ammoniumsalt of iodized benzene ring-containing N-carbonylsulfonamide, aniodized benzene ring-containing amine, and an iodized benzenering-containing ammonium salt exhibits a high sensitivity, low LWR,improved CDU, and wide process margin.

In one aspect, the invention provides a resist composition comprising aniodized base polymer, and at least one quencher selected from the groupconsisting of a sulfonium or ammonium salt of iodized benzenering-containing carboxylic acid, a sulfonium or ammonium salt of iodizedbenzene ring-containing N-carbonylsulfonamide, an iodized benzenering-containing amine, and an iodized benzene ring-containing ammoniumsalt.

Preferably, the sulfonium or ammonium salt of iodized benzenering-containing carboxylic acid, the sulfonium or ammonium salt ofiodized benzene ring-containing N-carbonylsulfonamide, the iodizedbenzene ring-containing amine, and the iodized benzene ring-containingammonium salt have the following formulae (A)-1 to (A)-4, respectively.

Herein R¹ is hydroxyl, fluorine, chlorine, bromine, amino, nitro, cyano,or a C₁-C₆ alkyl group, C₁-C₆ alkoxy group, C₂-C₆ acyloxy group or C₁-C₄alkylsulfonyloxy group, which may be substituted with halogen, or—NR^(1A)—C(═O)—R^(1B) or —NR^(1A)—C(═O)—O—R^(1B), R^(1A) is hydrogen ora C₁-C₆ alkyl group, R^(1B) is a C₁-C₆ alkyl group or C₂-C₈ alkenylgroup. R² is a single bond or a C₁-C₂₀ divalent linking group which maycontain ether bond, carbonyl moiety, ester bond, amide bond, sultonemoiety, lactam moiety, carbonate moiety, halogen, hydroxyl moiety orcarboxyl moiety. R³ is a C₁-C₁₀ alkyl group or C₆-C₁₀ aryl group, whichmay be substituted with amino, nitro, cyano, C₁-C₁₂ alkyl, C₁-C₁₂alkoxy, C₂-C₁₂ alkoxycarbonyl, C₂-C₁₂ acyl, C₂-C₁₂ acyloxy, hydroxyl orhalogen. R⁴ is a C₁-C₂₀ divalent hydrocarbon group which may contain anester bond or ether bond. R⁵ is hydrogen, nitro, or a C₁-C₂₀ monovalenthydrocarbon group which may contain hydroxyl, carboxyl, ether bond,ester bond, thiol, nitro, cyano, halogen or amino, with the proviso thatin case of p=1, groups R⁵ may bond together to form a ring with thenitrogen atom to which they are attached, the ring optionally containinga double bond, oxygen, sulfur or nitrogen; m is an integer of 1 to 5, nis an integer of 0 to 4, meeting 1≤m+n≤5, p is 1, 2 or 3, q is 1 or 2.A^(q−) is a carboxylate anion, fluorine-free sulfonimide anion,sulfonamide anion, or halide ion. X⁺ is a sulfonium cation having theformula (Aa) or ammonium cation having the formula (Ab):

Herein R⁶, R⁷ and R⁸ are each independently fluorine, chlorine, bromine,iodine, or a C₁-C₂₀ monovalent hydrocarbon group which may contain aheteroatom, R⁶ and R⁷ may bond together to form a ring with the sulfuratom to which they are attached. R⁹ to R¹² are each independentlyhydrogen or a C₁-C₂₄ monovalent hydrocarbon group which may containhalogen, hydroxyl, carboxyl, thiol, ether bond, ester bond, thioesterbond, thionoester bond, dithioester bond, amino, nitro, sulfone orferrocenyl, R⁹ and R¹⁰ may bond together to form a ring, R⁹ and R¹⁰taken together may form ═C(R^(9A))(R^(10A)), R^(9A) and R^(10A) are eachindependently hydrogen or a C₁-C₁₆ monovalent hydrocarbon group, R^(9A)and R^(10A) may bond together to form a ring with the carbon andnitrogen atoms to which they are attached, the ring optionallycontaining a double bond, oxygen, sulfur or nitrogen.

The resist composition may further comprise an acid generator capable ofgenerating sulfonic acid, imidic acid or methide acid.

In a preferred embodiment, the iodized base polymer comprises recurringunits having the formula (a1) or recurring units having the formula(a2).

Herein R^(A) is each independently hydrogen or methyl, R²¹ is a singlebond or methylene, R²² is hydrogen or a C₁-C₄ alkyl group, X¹ is asingle bond, ether bond, ester bond, amide bond, —C(═O)—O—R²³—,phenylene, -Ph-C(═O)—O—R²⁴—, or -Ph-R²⁵—O—C(═O)—R²⁶—, wherein Ph standsfor phenyl, R²³ is a C₁-C₁₀ alkanediyl group which may contain an etherbond or ester bond, R²⁴, R²⁵ and R²⁶ are each independently a singlebond or a C₁-C₆ straight or branched alkanediyl group, a is an integerof 1 to 5, preferably an integer of 1 to 3, b is an integer of 1 to 4,meeting 1≤a+b≤5.

Typically the resist composition contains an organic solvent.

In a preferred embodiment, the iodized base polymer further comprisesrecurring units having the formula (b1) or recurring units having theformula (b2).

Herein R^(A) is each independently hydrogen or methyl, Y¹ is a singlebond, phenylene, naphthylene, or a C₁-C₁₂ linking group containing anester bond or lactone ring, Y² is a single bond or ester bond, R³¹ andR³² are each independently an acid labile group, R³³ is fluorine,trifluoromethyl, cyano, a C₁-C₆ alkyl, C₁-C₆ alkoxy, C₂-C₇ acyl, C₂-C₇acyloxy, or C₂-C₇ alkoxycarbonyl group, R³⁴ is a single bond or C₁-C₆alkanediyl group in which some carbon may be replaced by an ether orester bond, c is 1 or 2, d is an integer of 0 to 4, meeting 1≤c+d≤5.

The resist composition may further comprise a dissolution inhibitor.

Typically, the resist composition is a chemically amplified positiveresist composition.

In another preferred embodiment, the iodized base polymer is free of anacid labile group. The resist composition may further comprise acrosslinker. Typically, the resist composition is a chemically amplifiednegative resist composition.

The resist composition may further comprise an iodine-free quencher.

The resist composition may further comprise a surfactant.

In a further preferred embodiment, the iodized base polymer furthercomprises recurring units of at least one type selected from recurringunits having the formulae (g1) to (g3).

Herein R^(A) is each independently hydrogen or methyl. Z¹ is a singlebond, phenylene, —O—Z¹²—, —C(═O)—Z¹¹—Z¹²—, Z¹¹ is —O— or —NH—, Z¹² is aC₁-C₆ alkanediyl group, C₂-C₆ alkenediyl group or phenylene group, whichmay contain a carbonyl moiety, ester bond, ether bond or hydroxylmoiety. Z² is a single bond, —Z²¹—C(═O)—O—, —Z²¹—O—, or —Z²¹—O—C(═O)—,Z²¹ is a C₁-C₁₂ alkanediyl group which may contain a carbonyl moiety,ester bond or ether bond. Z³ is a single bond, methylene, ethylene,phenylene, fluorinated phenylene, —O—Z³²—, or —C(═O)—Z³¹—Z³²—, Z³¹ is—O— or —NH—, Z³² is a C₁-C₆ alkanediyl group, phenylene, fluorinatedphenylene, trifluoromethyl-substituted phenylene group, or C₂-C₆alkenediyl group, which may contain a carbonyl moiety, ester bond, etherbond or hydroxyl moiety. R⁴¹ to R⁴⁸ are each independently a C₁-C₂₀monovalent hydrocarbon group which may contain a heteroatom, any two ofR⁴³, R⁴⁴ and R⁴⁵ or any two of R⁴⁶, R⁴⁷ and R⁴⁸ may bond together toform a ring with the sulfur atom to which they are attached. “A” ishydrogen or trifluoromethyl. Q⁻ is a non-nucleophilic counter ion.

In another aspect, the invention provides a pattern forming processcomprising the steps of applying the resist composition defined above toform a resist film on a substrate, exposing the resist film tohigh-energy radiation, and developing the exposed resist film in adeveloper.

Preferably, the high-energy radiation is ArF excimer laser of wavelength193 nm, KrF excimer laser of wavelength 248 nm, EB, or EUV of wavelength3 to 15 nm.

Advantageous Effects of Invention

A resist composition comprising an iodized polymer and a quencherselected from a sulfonium or ammonium salt of iodized benzenering-containing carboxylic acid, a sulfonium or ammonium salt of iodizedbenzene ring-containing N-carbonylsulfonamide, an iodized benzenering-containing amine, and an iodized benzene ring-containing ammoniumsalt has the advantage of controlled acid diffusion due to the highatomic weight of iodine. Since iodine is highly absorptive to EUV ofwavelength 13.5 nm, it effectively generates secondary electrons duringexposure. This contributes to a higher sensitivity than a combination ofan iodized polymer with an iodine-free quencher. Thus, a resist materialhaving a high sensitivity, low LWR and improved CDU may be designed.

DESCRIPTION OF EMBODIMENTS

As used herein, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. The notation(C_(n)-C_(m)) means a group containing from n to m carbon atoms pergroup. As used herein, the term “iodized” or “fluorinated” indicatesthat a compound contains iodine or fluorine. Me stands for methyl, Acfor acetyl, and Ph for phenyl.

The abbreviations and acronyms have the following meaning.

-   -   EB: electron beam    -   EUV: extreme ultraviolet    -   Mw: weight average molecular weight    -   Mn: number average molecular weight    -   Mw/Mn: molecular weight distribution or dispersity    -   GPC: gel permeation chromatography    -   PEB: post-exposure bake    -   PAG: photoacid generator    -   LWR: line width roughness    -   CDU: critical dimension uniformity        Resist Composition

One embodiment of the invention is a resist composition comprising aniodized base polymer and at least one quencher selected from the groupconsisting of a sulfonium or ammonium salt of iodized benzenering-containing carboxylic acid, a sulfonium or ammonium salt of iodizedbenzene ring-containing N-carbonylsulfonamide, an iodized benzenering-containing amine, and an iodized benzene ring-containing ammoniumsalt, which are collectively referred to as “iodized benzenering-containing quencher,” hereinafter. The quencher traps the acidgenerated upon radiation exposure. An acid generator capable ofgenerating a sulfonic acid, imide acid or methide acid may be added tothe resist composition while a polymer-bound acid generator may also beused.

In the resist composition, the base polymer contains iodine. Sinceiodine is highly absorptive to radiation, the base polymer generatessecondary electrons upon exposure. The energy of secondary electrons istransferred to the acid generator to promote the efficiency of acidgeneration. As the efficiency of acid generation increases, the aciddiffusion becomes more active. This invites a higher sensitivity anddegraded CDU or LWR at the same time, failing to escape from thetradeoff relationship of sensitivity to CDU or LWR.

It is the iodized benzene ring-containing quencher that can effectivelysuppress the acid diffusion. The quencher suppresses the diffusion ofacid which is efficiently generated by more secondary electronsgenerated from the iodized polymer, thereby achieving a high sensitivityand improved CDU or low LWR at the same time. It becomes possible toescape from the outstanding tradeoff relationship. Since the iodizedbenzene ring-containing quencher itself is highly absorptive, it alsogenerates secondary electrons to promote decomposition of the acidgenerator.

The iodized benzene ring-containing quencher exerts the desired LWR orCDU improving effect, which may stand good either in positive andnegative tone pattern formation by aqueous alkaline development or innegative tone pattern formation by organic solvent development.

Iodized Benzene Ring-Containing Quencher

The iodized benzene ring-containing quencher is preferably selected fromcompounds having the following formulae (A)-1 to (A)-4.

In formulae (A)-1 and (A)-2, R¹ is hydroxyl, fluorine, chlorine,bromine, amino, nitro, cyano, or a C₁-C₆ alkyl group, C₁-C₆ alkoxygroup, C₂-C₆ acyloxy group or C₁-C₄ alkylsulfonyloxy group, which may besubstituted with halogen, or —NR^(1A)—C(═O)—R^(1B) or—NR^(1A)—C(═O)—O—R^(1B), wherein R^(1A) is hydrogen or a C₁-C₆ alkylgroup, and R^(1B) is a C₁-C₆ alkyl group or C₂-C₈ alkenyl group.

The C₁-C₆ alkyl group may be straight, branched or cyclic and examplesthereof include methyl, ethyl, n-propyl, isopropyl, cyclopropyl,n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl,cyclopentyl, n-hexyl and cyclohexyl. The alkyl moiety of the C₁-C₆alkoxy group is as exemplified for the alkyl group; the alkyl moiety ofthe C₂-C₆ acyloxy group is as exemplified for the alkyl group, but of 1to 5 carbon atoms; the alkyl moiety of the C₁-C₄ alkylsulfonyloxy groupis as exemplified for the alkyl group, but of 1 to 4 carbon atoms. TheC₂-C₈ alkenyl group may be straight, branched or cyclic and examplesthereof include vinyl, 1-propenyl, 2-propenyl, butenyl, hexenyl, andcyclohexenyl.

R¹ is preferably fluorine, chlorine, bromine, hydroxyl, amino, C₁-C₃alkyl, C₁-C₃ alkoxy, C₂-C₄ acyloxy, —NR^(1A)—C(═O)—R^(1B), or—NR^(1A)—C(═O)—O—R^(1B).

In formulae (A)-1 and (A)-2, R² is a single bond or a C₁-C₂₀ divalentlinking group which may contain an ether bond, carbonyl moiety, esterbond, amide bond, sultone moiety, lactam moiety, carbonate moiety,halogen, hydroxyl moiety or carboxyl moiety.

In formula (A)-2, R³ is a C₁-C₁₀ alkyl group or C₆-C₁₀ aryl group, whichmay be substituted with amino, nitro, cyano, C₁-C₁₂ alkyl, C₁-C₁₂alkoxy, C₂-C₁₂ alkoxycarbonyl, C₂-C₁₂ acyl, C₂-C₁₂ acyloxy, hydroxyl orhalogen.

The C₁-C₁₀ alkyl group may be straight, branched or cyclic and examplesthereof include n-heptyl, n-octyl, n-nonyl, n-decyl, norbornyl andadamantyl as well as those exemplified above for the C₁-C₆ alkyl group.Examples of the C₆-C₁₀ aryl group include phenyl, tolyl, xylyl,1-naphthyl and 2-naphthyl. The C₁-C₁₂ alkyl group may be straight,branched or cyclic and examples thereof include n-undecyl and n-dodecylas well as those exemplified above for the C₁-C₁₀ alkyl group. The alkylmoiety of the C₁-C₁₂ alkoxy group is as exemplified above for the C₁-C₁₂alkyl group; the alkyl moiety of the C₂-C₁₂ alkoxycarbonyl group, C₂-C₁₂acyl group, and C₂-C₁₂ acyloxy group is as exemplified above for theC₁-C₁₂ alkyl group, but of 1 to 11 carbon atoms.

In formulae (A)-3 and (A)-4, R⁴ is a C₁-C₂₀ divalent hydrocarbon group.The divalent hydrocarbon group may be straight, branched or cyclic.Examples thereof include straight or branched alkanediyl groups such asmethylene, ethylene, propane-1,2-diyl, propane-1,3-diyl,butane-1,2-diyl, butane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl,hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl, nonane-1,9-diyl,decane-1,10-diyl, undecane-1,11-diyl, dodecane-1,12-diyl; C₃-C₂₀ cyclicalkanediyl groups such as cyclopentanediyl, cyclohexanediyl,norbornanediyl, and adamantanediyl; C₂-C₂₀ alkenediyl groups such asvinylene and propene-1,3-diyl; and C₆-C₂₀ arylene groups such asphenylene and naphthylene, and mixtures thereof. The divalenthydrocarbon group may contain an ester bond and/or ether bond.

In formulae (A)-3 and (A)-4, R⁵ is hydrogen, nitro, or a C₁-C₂₀monovalent hydrocarbon group. The C₁-C₂₀ monovalent hydrocarbon groupmay be straight, branched or cyclic. Examples thereof include straightor branched C₁-C₂₀ alkyl groups such as methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl,n-octyl, n-nonyl, n-decyl, undecyl, dodecyl, tridecyl, tetradecyl,pentadecyl, heptadecyl, octadecyl, nonadecyl and icosyl; C₃-C₂₀ cyclicalkyl groups such as cyclopropyl, cyclopentyl, cyclohexyl,cyclopropylmethyl, 4-methylcyclohexyl, cyclohexylmethyl, norbornyl,adamantyl; C₂-C₂₀ alkenyl groups such as vinyl, propenyl, butenyl,hexenyl; C₃-C₂₀ cyclic alkenyl groups such as cyclohexenyl andnorbornenyl; C₂-C₂₀ alkynyl groups such as ethynyl, propynyl, butynyl,2-cyclohexylethynyl, 2-phenylethynyl; C₆-C₂₀ aryl groups such as phenyl,methylphenyl, ethylphenyl, n-propylphenyl, isopropylphenyl,n-butylphenyl, isobutylphenyl, sec-butylphenyl, tert-butylphenyl,naphthyl, methylnaphthyl, ethylnaphthyl, n-propylnaphthyl,isopropylnaphthyl, n-butylnaphthyl, isobutylnaphthyl, sec-butylnaphthyl,tert-butylnaphthyl; C₇-C₂₀ aralkyl groups such as benzyl and phenethyl.The monovalent hydrocarbon group may contain hydroxyl, carboxyl, etherbond, ester bond, thiol, nitro, cyano, halogen or amino, or a mixturethereof. In case of p=1, groups R⁵ may bond together to form a ring withthe nitrogen atom to which they are attached, and the relevant ring maycontain a double bond, oxygen, sulfur or nitrogen.

In formulae (A)-1 to (A)-4, m is an integer of 1 to 5, and n is aninteger of 0 to 4, meeting 1≤m+n≤5. In formulae (A)-3 and (A)-4, p is 1,2 or 3, and q is 1 or 2.

Examples of the anion of the salt having formula (A)-1 are shown below,but not limited thereto.

Examples of the anion of the salt having formula (A)-2 are shown below,but not limited thereto.

In formulae (A)-1 and (A)-2, X⁺ is a sulfonium cation having the formula(Aa) or ammonium cation having the formula (Ab).

In formula (Aa), R⁶, R⁷ and R⁸ are each independently fluorine,chlorine, bromine, iodine, or a C₁-C₂₀ monovalent hydrocarbon groupwhich may contain a heteroatom. R⁶ and R⁷ may bond together to form aring with the sulfur atom to which they are attached. The C₁-C₂₀monovalent hydrocarbon group may be straight, branched or cyclic, andexamples thereof include C₁-C₂₀ alkyl, C₆-C₂₀ aryl, and C₇-C₂₀ aralkylgroups. In these groups, some or all hydrogen may be substituted byhydroxyl, carboxyl, halogen, cyano, nitro, sultone, sulfone, orsulfonium salt-containing moiety, or an ether bond, ester bond, amidebond, carbonyl moiety, carbonate moiety or sulfonate bond may intervenebetween carbon atoms.

Preferred examples of the sulfonium cation having formula (Aa) are thosehaving the formulae (Aa)-1 and (Aa)-2.

In formulae (Aa)-1 and (Aa)-2, R¹³ to R¹⁸ are each independently aC₁-C₁₄ monovalent hydrocarbon group. Examples of the monovalenthydrocarbon group include C₁-C₁₄ alkyl, C₂-C₁₄ alkenyl, C₆-C₁₄ aryl, andC₇-C₁₄ aralkyl groups. In these groups, some or all hydrogen may besubstituted by hydroxyl, carboxyl, halogen, cyano, nitro, sultone,sulfone, or sulfonium salt-containing moiety, or some carbon may bereplaced by ether bond, ester bond, carbonyl, amide bond, carbonate orsulfonic ester bond. L is a single bond, methylene, ether bond,thioether bond, or carbonyl group. The subscripts z¹ to z⁶ are eachindependently an integer of 0 to 5. Examples of the alkyl, alkenyl, aryland aralkyl groups are as exemplified above for R⁵.

Examples of the sulfonium cation having formula (Aa) are shown below,but not limited thereto.

In formula (Ab), R⁹ to R¹² are each independently hydrogen or a C₁-C₂₄monovalent hydrocarbon group which may contain halogen, hydroxyl,carboxyl, thiol, ether bond, ester bond, thioester bond, thionoesterbond, dithioester bond, amino, nitro, sulfone or ferrocenyl. R⁹ and R¹⁰may bond together to form a ring, or R⁹ and R¹⁰ taken together may form═C(R^(9A))(R^(10A)), wherein R^(9A) and R^(10A) are each independentlyhydrogen or a C₁-C₁₆ monovalent hydrocarbon group, R^(9A) and R^(10A)may bond together to form a ring with the carbon and nitrogen atoms towhich they are attached, and the relevant ring may contain a doublebond, oxygen, sulfur or nitrogen.

The C₁-C₂₄ monovalent hydrocarbon group may be straight, branched orcyclic and examples thereof include C₁-C₂₄ alkyl, C₂-C₂₄ alkenyl, C₂-C₂₄alkynyl, C₆-C₂₀ aryl, and C₇-C₂₀ aralkyl groups, and mixtures thereof.Examples of the alkyl, alkenyl, alkynyl, aryl and aralkyl groups are asexemplified above for R⁵.

Examples of the ammonium cation having formula (Ab) are shown below, butnot limited thereto.

Examples of the amine compound having formula (A)-3 are shown below, butnot limited thereto.

Examples of the cation of the ammonium salt having formula (A)-4 areshown below, but not limited thereto.

In formula (A)-4, A^(q−) is a carboxylate anion, fluorine-freesulfonimide anion, sulfonamide anion, or halide ion.

Examples of the carboxylate anion are shown below, but not limitedthereto.

Examples of the fluorine-free sulfonimide anion are shown below, but notlimited thereto.

Examples of the sulfonamide anion are shown below, but not limitedthereto.

Exemplary of the halide ion are fluoride, chloride, bromide and iodideions.

In the resist composition, it is preferred in view of sensitivity andacid diffusion suppressing effect to use the iodized benzenering-containing quencher in an amount of 0.001 to 30 parts by weight,more preferably 0.005 to 20 parts by weight per 100 parts by weight ofthe base polymer. The iodized benzene ring-containing quencher may beused alone or in admixture.

Base Polymer

The base polymer in the resist composition is an iodized polymer,referred to as Polymer A, hereinafter. Polymer A preferably comprisesrecurring units having the formula (a1) or recurring units having theformula (a2). These units are simply referred to as recurring units (a1)and (a2).

In formulae (a1) and (a2), R^(A) is each independently hydrogen ormethyl. R²¹ is a single bond or methylene. R²² is hydrogen or a C₁-C₄alkyl group. The alkyl group may be straight, branched or cyclic andpreferably straight or branched. X¹ is a single bond, ether bond, esterbond, amide bond, —C(═O)—O—R²³—, phenylene, -Ph-C(═O)—O—R²⁴—, or-Ph-R²⁵—O—C(═O)—R²⁶—, wherein Ph is phenylene, R²³ is a C₁-C₁₀alkanediyl group which may be straight, branched or cyclic, and containan ether bond or ester bond, R²⁴, R²⁵ and R²⁶ are each independently asingle bond or a C₁-C₆ straight or branched alkanediyl group.

In formula (a1), “a” is an integer of 1 to 5, b is an integer of 0 to 4,and 1≤a+b≤5. It is preferred that b be an integer of 1 to 3 and “a” bean integer of 1 to 3 because the inclusion of hydroxyl group ensuresmore efficient generation of secondary electrons, leading to a highersensitivity.

Examples of the monomer from which recurring units (a1) are derived areshown below, but not limited thereto. Herein R^(A) is as defined above.

Examples of the monomer from which recurring units (a2) are derived areshown below, but not limited thereto. Herein R^(A) is as defined above.

The recurring units (a1) or (a2) may be used alone or in admixture, andthe recurring units (a1) and (a2) may be used in combination.

In one embodiment wherein the resist composition is of positive tone,preferably Polymer A further comprises recurring units having an acidlabile group. The preferred recurring units having an acid labile groupare recurring units having the formula (b1), which are referred to asrecurring units (b1), or recurring units having the formula (b2), whichare referred to as recurring units (b2), hereinafter. In anotherembodiment wherein the resist composition is of negative tone,preferably Polymer A is free of recurring units having an acid labilegroup.

In formulae (b1) and (b2), R^(A) is each independently hydrogen ormethyl. Y¹ is a single bond, phenylene group, naphthylene group, or aC₁-C₁₂ linking group containing an ester bond or lactone ring. Y² is asingle bond or ester bond. R³¹ and R³² are each independently an acidlabile group. R³³ is fluorine, trifluoromethyl, cyano, C₁-C₆ alkyl,C₁-C₆ alkoxy, C₂-C₇ acyl, C₂-C₇ acyloxy, or C₂-C₇ alkoxycarbonyl group.R³⁴ is a single bond or a C₁-C₆ alkanediyl group in which some carbonmay be replaced by an ether or ester bond, c is 1 or 2, d is an integerof 0 to 4, and 1≤c+d≤5. The alkyl, alkoxy, acyl, acyloxy andalkoxycarbonyl groups may be straight, branched or cyclic. The C₁-C₆alkanediyl groups are preferably straight or branched.

Examples of the monomer from which recurring units (b1) are derived areshown below, but not limited thereto. Herein R^(A) and R³¹ are asdefined above.

Examples of the monomer from which recurring units (b2) are derived areshown below, but not limited thereto. Herein R^(A) and R³² are asdefined above.

The acid labile groups represented by R³¹ and R³² in the recurring units(b1) and (b2) may be selected from a variety of such groups, forexample, those groups described in JP-A 2013-080033 (U.S. Pat. No.8,574,817) and JP-A 2013-083821 (U.S. Pat. No. 8,846,303).

Typical of the acid labile group are groups of the following formulae(AL-1) to (AL-3).

In formulae (AL-1) and (AL-2), R^(L1) and R^(L2) are each independentlya monovalent hydrocarbon group which may contain a heteroatom such asoxygen, sulfur, nitrogen or fluorine. The monovalent hydrocarbon groupsmay be straight, branched or cyclic, with alkyl groups of 1 to 40 carbonatoms, especially 1 to 20 carbon atoms being preferred. In formula(AL-1), x¹ is an integer of 0 to 10, especially 1 to 5.

In formula (AL-2), R^(L3) and R^(L4) are each independently hydrogen ora monovalent hydrocarbon group which may contain a heteroatom such asoxygen, sulfur, nitrogen or fluorine. The monovalent hydrocarbon groupsmay be straight, branched or cyclic, with C₁-C₂₀ alkyl groups beingpreferred. Any two of R^(L2), R^(L3) and R^(L4) may bond together toform a ring with the carbon atom or carbon and oxygen atoms to whichthey are attached. The ring contains 3 to 20 carbon atoms, preferably 4to 16 carbon atoms, and is typically alicyclic.

In formula (AL-3), R^(L5), R^(L6) and R^(L7) are each independently amonovalent hydrocarbon group which may contain a heteroatom such asoxygen, sulfur, nitrogen or fluorine. The monovalent hydrocarbon groupsmay be straight, branched or cyclic, with C₁-C₂₀ alkyl groups beingpreferred. Any two of R^(L5), R^(L6) and R^(L7) may bond together toform a ring with the carbon atom to which they are attached. The ringcontains 3 to 20 carbon atoms, preferably 4 to 16 carbon atoms and istypically alicyclic.

Polymer A may further comprise recurring units (c) having a phenolichydroxyl group as an adhesive group. The recurring units (c) may be usedalone or in admixture.

Examples of the monomers from which recurring units (c) are derived aregiven below, but not limited thereto. Herein R^(A) is as defined above.

Polymer A may further comprise recurring units (d) having anotheradhesive group selected from hydroxyl (other than the phenolichydroxyl), carboxyl, lactone ring, ether bond, ester bond, carbonyl andcyano groups. The recurring units (d) may be used alone or in admixture.

Examples of the monomer from which recurring units (d) are derived aregiven below, but not limited thereto. Herein R^(A) is as defined above.

In another preferred embodiment, Polymer A may further compriserecurring units (e) selected from units of indene, benzofuran,benzothiophene, acenaphthylene, chromone, coumarin, and norbornadiene,or derivatives thereof. The recurring units (e) may be used alone or inadmixture.

Suitable monomers from which recurring units (e) are derived areexemplified below, but not limited thereto.

Polymer A may further comprise recurring units (f) which are derivedfrom styrene, vinylnaphthalene, vinylanthracene, vinylpyrene,methyleneindene, vinylpyridine, and vinylcarbazole. The recurring units(f) may be used alone or in admixture.

In a further embodiment, Polymer A may further comprise recurring units(g) derived from a sulfonic acid onium salt having a polymerizableunsaturated bond. JP-A 2005-084365 discloses sulfonium and iodoniumsalts having a polymerizable unsaturated bond capable of generating asulfonic acid. JP-A 2006-178317 discloses a sulfonium salt havingsulfonic acid directly attached to the main chain.

The preferred recurring units (g) are recurring units having thefollowing formulae (g1), (g2) and (g3). These units are simply referredto as recurring units (g1), (g2) and (g3), which may be used alone or incombination of two or more types.

In formulae (g1) to (g3), R^(A) is each independently hydrogen ormethyl. Z¹ is a single bond, phenylene group, —O—Z¹²—, or—C(═O)—Z¹¹—Z¹²—, wherein Z¹¹ is —O— or —NH—, and Z¹² is a C₁-C₆alkanediyl, C₂-C₆ alkenediyl or phenylene group, which may contain acarbonyl, ester bond, ether bond or hydroxyl moiety. Z² is a singlebond, —Z²¹—C(═O)—O—, —Z²¹—O— or —Z²¹—O—C(═O)—, wherein Z²¹ is a C₁-C₁₂alkanediyl group which may contain a carbonyl moiety, ester bond orether bond. Z³ is a single bond, methylene, ethylene, phenylene orfluorinated phenylene group, —O—Z³²—, or —C(═O)—Z³¹—Z³²—, wherein Z³¹ is—O— or —NH—, and Z³² is a C₁-C₆ alkanediyl, phenylene, fluorinatedphenylene, trifluoromethyl-substituted phenylene, or C₂-C₆ alkenediylgroup, which may contain a carbonyl, ester bond, ether bond or hydroxylmoiety.

In formulae (g1) to (g3), R⁴¹ to R⁴⁸ are each independently a C₁-C₂₀monovalent hydrocarbon group which may contain a heteroatom. Any two ofR⁴³, R⁴⁴ and R⁴⁵ or any two of R⁴⁶, R⁴⁷ and R⁴⁸ may bond together toform a ring with the sulfur atom to which they are attached. Thesulfonium cation in formulae (g2) and (g3) is preferably selected fromthe cations having the foregoing formula (Aa), and examples thereof areas exemplified above for the sulfonium cation in formula (Aa).

In formula (g1), Q⁻ is a non-nucleophilic counter ion. Examples of thenon-nucleophilic counter ion include halide ions such as chloride andbromide ions; fluoroalkylsulfonate ions such as triflate,1,1,1-trifluoroethanesulfonate, and nonafluorobutanesulfonate;arylsulfonate ions such as tosylate, benzenesulfonate,4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate;alkylsulfonate ions such as mesylate and butanesulfonate; imide ionssuch as bis(trifluoromethylsulfonyl)imide,bis(perfluoroethylsulfonyl)imide and bis(perfluorobutylsulfonyl)imide;methide ions such as tris(trifluoromethylsulfonyl)methide andtris(perfluoroethylsulfonyl)methide.

Also included are sulfonate ions having fluorine substituted atα-position as represented by the formula (K-1) and sulfonate ions havingfluorine substituted at α- and β-positions as represented by the formula(K-2).

In formula (K-1), R⁵¹ is hydrogen, or a C₁-C₂₀ alkyl group, C₂-C₂₀alkenyl group, or C₆-C₂₀ aryl group, which may contain an ether bond,ester bond, carbonyl moiety, lactone ring, or fluorine atom. The alkyland alkenyl groups may be straight, branched or cyclic.

In formula (K-2), R⁵² is hydrogen, or a C₁-C₃₀ alkyl group, C₂-C₂₀ acylgroup, C₂-C₂₀ alkenyl group, C₆-C₂₀ aryl group or C₆-C₂₀ aryloxy group,which may contain an ether bond, ester bond, carbonyl moiety or lactonering. The alkyl, acyl and alkenyl groups may be straight, branched orcyclic.

Examples of the monomer from which recurring unit (g1) is derived areshown below, but not limited thereto. R^(A) and Q⁻ are as defined above.

Examples of the monomer from which recurring unit (g2) is derived areshown below, but not limited thereto. R^(A) is as defined above.

Examples of the monomer from which recurring unit (g3) is derived areshown below, but not limited thereto. R^(A) is as defined above.

Recurring unit (g) functions as a polymer-bound acid generator. Theattachment of an acid generator to the polymer main chain is effectivein restraining acid diffusion, thereby preventing a reduction ofresolution due to blur by acid diffusion. Also edge roughness isimproved since the acid generator is uniformly distributed. Where a basepolymer comprising recurring units (g) is used, an acid generatorcapable of generating a strong acid (or addition type, to be describedlater) may be omitted.

Polymer A for formulating the positive resist composition comprisesrecurring units (a1) or (a2) containing iodine and additionallyrecurring units (b1) or (b2) having an acid labile group, and optionallyrecurring units (c), (d), (e), (f), and (g). A fraction of units (a1),(a2), (b1), (b2), (c), (d), (e), (f) and (g) is: preferably 0≤a1<1.0,0<a2<1.0, 0<a1+a2<1.0, 0≤b1<1.0, 0≤b2<1.0, 0<b1+b2<1.0, 0≤c≤0.9,0≤d≤0.9, 0≤e≤0.8, 0≤f≤0.8, and 0≤g≤0.5; more preferably 0≤a1≤0.9,0≤a2≤0.9, 0.1≤a1+a2≤0.9, 0≤b1≤0.9, 0≤b2≤0.9, 0.1≤b1+b2≤0.9, 0≤c≤0.8,0≤d≤0.8, 0≤e≤0.7, 0≤f≤0.7, and 0≤g≤0.4; and even more preferably0≤a1≤0.8, 0≤a2≤0.8, 0.1≤a1+a2≤0.8, 0≤b1≤0.8, 0≤b2≤0.8, 0.1≤b1+b2≤0.8,0≤c≤0.75, 0≤d≤0.75, 0≤e≤0.6, 0≤f≤0.6, and 0≤g≤0.3. Notably, g=g1+g2+g3,meaning that unit (g) is at least one of units (g1) to (g3), anda1+a2+b1+b2+c+d+e+f+g=1.0.

For Polymer A for formulating the negative resist composition, an acidlabile group is not necessarily essential. The polymer comprises iodizedrecurring units (a1) or (a2) and recurring units (c), and optionallyrecurring units (d), (e), (f), and/or (g). A fraction of these units is:preferably 0≤a1<1.0, 0≤a2<1.0, 0<a1+a2<1.0, 0<c<1.0, 0≤d≤0.9, 0≤e≤0.8,0≤f≤0.8, and 0≤g≤0.5; more preferably 0≤a1≤0.8, 0≤a2≤0.8, 0.1≤a1+a2≤0.8,0.2≤c≤0.9, 0≤d≤0.8, 0≤e≤0.7, 0≤f≤0.7, and 0≤g≤0.4; and even morepreferably 0≤a1≤0.7, 0≤a2≤0.7, 0.2≤a1+a2≤0.7, 0.3≤c≤0.8, 0≤d≤0.75,0≤e≤0.6, 0≤f≤0.6, and 0≤g≤0.3. Notably, g=g1+g2+g3, meaning that unit(g) is at least one of units (g1) to (g3), and a1+a2+c+d+e+f+g=1.0.

Polymer A may be synthesized by any desired methods, for example, bydissolving one or more monomers selected from the monomers correspondingto the foregoing recurring units in an organic solvent, adding a radicalpolymerization initiator thereto, and heating for polymerization.Examples of the organic solvent which can be used for polymerizationinclude toluene, benzene, tetrahydrofuran, diethyl ether, and dioxane.Examples of the polymerization initiator used herein include2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the reaction temperature is 50 to 80° C., and the reactiontime is 2 to 100 hours, more preferably 5 to 20 hours.

In the case of a monomer having a hydroxyl group, the hydroxyl group maybe replaced by an acetal group susceptible to deprotection with acid,typically ethoxyethoxy, prior to polymerization, and the polymerizationbe followed by deprotection with weak acid and water. Alternatively, thehydroxyl group may be replaced by an acetyl, formyl, pivaloyl or similargroup prior to polymerization, and the polymerization be followed byalkaline hydrolysis.

When hydroxystyrene or hydroxyvinylnaphthalene is copolymerized, analternative method is possible. Specifically, acetoxystyrene oracetoxyvinylnaphthalene is used instead of hydroxystyrene orhydroxyvinylnaphthalene, and after polymerization, the acetoxy group isdeprotected by alkaline hydrolysis, for thereby converting the polymerproduct to hydroxystyrene or hydroxyvinylnaphthalene. For alkalinehydrolysis, a base such as aqueous ammonia or triethylamine may be used.Preferably the reaction temperature is −20° C. to 100° C., morepreferably 0° C. to 60° C., and the reaction time is 0.2 to 100 hours,more preferably 0.5 to 20 hours.

Polymer A should preferably have a weight average molecular weight (Mw)in the range of 1,000 to 500,000, and more preferably 2,000 to 30,000,as measured by GPC versus polystyrene standards using tetrahydrofuran(THF) solvent. A polymer with a Mw in the range is heat resistant andalkaline soluble.

If a polymer has a wide molecular weight distribution or dispersity(Mw/Mn), which indicates the presence of lower and higher molecularweight polymer fractions, there is a possibility that foreign matter isleft on the pattern or the pattern profile is degraded. The influencesof Mw and Mw/Mn become stronger as the pattern rule becomes finer.Therefore, Polymer A should preferably have a narrow dispersity (Mw/Mn)of 1.0 to 2.0, especially 1.0 to 1.5, in order to provide a resistcomposition suitable for micropatterning to a small feature size.

The base polymer may be a blend of two or more Polymers A which differin compositional ratio, Mw or Mw/Mn. Also the base polymer may or maynot contain a polymer different from Polymer A, although it is preferredthat the base polymer be free of a different polymer.

Acid Generator

The resist composition may further contain an acid generator, referredto as acid generator of addition type. With the acid generator added,the resist composition has a higher sensitivity and more improvedproperties. Where the base polymer contains recurring units (g), i.e.,is a polymer-bound acid generator, the acid generator of addition typemay be omitted.

The acid generator is typically a compound (PAG) capable of generatingan acid upon exposure to actinic ray or radiation. Although the PAG usedherein may be any compound capable of generating an acid upon exposureto high-energy radiation, those compounds capable of generating sulfonicacid, imide acid (imidic acid) or methide acid are preferred. SuitablePAGs include sulfonium salts, iodonium salts, sulfonyldiazomethane,N-sulfonyloxyimide, and oxime-O-sulfonate acid generators. ExemplaryPAGs are described in U.S. Pat. No. 7,537,880 (JP-A 2008-111103,paragraphs [0122]-[0142]).

Also sulfonium salts having the formula (1-1) and iodonium salts havingthe formula (1-2) are useful PAGs.

In formulae (1-1) and (1-2), R¹⁰¹ to R¹⁰⁵ are each independently aC₁-C₂₀ monovalent hydrocarbon group which may contain a heteroatom. Anytwo of R¹⁰¹, R¹⁰² and R¹⁰³ may bond together to form a ring with thesulfur atom to which they are attached. The monovalent hydrocarbon groupmay be straight, branched or cyclic, and examples thereof are asexemplified above for R⁶ to R⁸ in formula (Aa).

Examples of the cation of the sulfonium salt having formula (1-1) are asexemplified above for the sulfonium cation having formula (Aa).

Examples of the cation of the iodonium salt having formula (1-2) areshown below, but not limited thereto.

In formulae (1-1) and (1-2), X⁻ is an anion selected from the formulae(1A) to (1D).

In formula (1A), R^(fa) is fluorine or a C₁-C₄₀ monovalent hydrocarbongroup which may contain a heteroatom. The monovalent hydrocarbon groupmay be straight, branched or cyclic and examples thereof are as will beexemplified below for R¹⁷.

Of the anions of formula (1A), a structure having formula (1A′) ispreferred.

In formula (1A′), R¹⁰⁶ is hydrogen or trifluoromethyl, preferablytrifluoromethyl. R¹⁰⁷ is a C₁-C₃₈ monovalent hydrocarbon group which maycontain a heteroatom. Suitable heteroatoms include oxygen, nitrogen,sulfur and halogen, with oxygen being preferred. Of the monovalenthydrocarbon groups, those of 6 to 30 carbon atoms are preferred becausea high resolution is available in fine pattern formation.

The monovalent hydrocarbon group may be straight, branched or cyclic.

Examples thereof include straight or branched alkyl groups such asmethyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl,tert-butyl, pentyl, neopentyl, cyclopentyl, hexyl, cyclohexyl, heptyl,2-ethylhexyl, nonyl, undecyl, tridecyl, pentadecyl, heptadecyl,icosanyl; monovalent saturated alicyclic hydrocarbon groups such as1-adamantyl, 2-adamantyl, 1-adamantylmethyl, norbornyl, norbornylmethyl,tricyclodecanyl, tetracyclododecanyl, tetracyclododecanylmethyl,dicyclohexylmethyl; monovalent unsaturated aliphatic hydrocarbon groupssuch as allyl and 3-cyclohexenyl; aryl groups such as phenyl, 1-naphthyland 2-naphthyl; aralkyl groups such as benzyl and diphenylmethyl.Exemplary heteroatom-containing monovalent hydrocarbon groups aretetrahydrofuryl, methoxymethyl, ethoxymethyl, methylthiomethyl,acetamidomethyl, trifluoroethyl, (2-methoxyethoxy)methyl, acetoxymethyl,2-carboxy-1-cyclohexyl, 2-oxopropyl, 4-oxo-1-adamantyl, and3-oxocyclohexyl. Also included are the foregoing groups in which somehydrogen is substituted by a moiety containing a heteroatom such asoxygen, sulfur, nitrogen or halogen, or in which some carbon is replacedby a moiety containing a heteroatom such as oxygen, sulfur or nitrogen,so that the group may contain a hydroxyl, cyano, carbonyl, ether bond,ester bond, sulfonic acid ester bond, carbonate, lactone ring, sultonering, carboxylic anhydride or haloalkyl moiety.

With respect to the synthesis of the sulfonium salt having an anion offormula (1A′), reference is made to JP-A 2007-145797, JP-A 2008-106045,JP-A 2009-007327, and JP-A 2009-258695. Also useful are the sulfoniumsalts described in JP-A 2010-215608, JP-A 2012-041320, JP-A 2012-106986,and JP-A 2012-153644.

Examples of the anion having formula (1A) are shown below, but notlimited thereto.

In formula (1B), R^(fb1) and R^(fb2) are each independently fluorine ora C₁-C₄₀ monovalent hydrocarbon group which may contain a heteroatom.The monovalent hydrocarbon group may be straight, branched or cyclic andexamples thereof are as exemplified above for R¹⁰⁷. Preferably R^(fb1)and R^(fb2) each are fluorine or a straight C₁-C₄ fluorinated alkylgroup. A pair of R^(fb1) and R^(fb2) may bond together to form a ringwith the linkage (—CF₂—SO₂—N⁻—SO₂—CF₂—) to which they are attached, andpreferably the pair is a fluorinated ethylene or fluorinated propylenegroup.

In formula (1C), R^(fc1), R^(fc2) and R^(fc3) are each independentlyfluorine or a C₁-C₄₀ monovalent hydrocarbon group which may contain aheteroatom. The monovalent hydrocarbon group may be straight, branchedor cyclic and examples thereof are as exemplified above for R¹⁰⁷.Preferably R^(fc1), R^(fc2) and R^(fc3) each are fluorine or a straightC₁-C₄ fluorinated alkyl group. A pair of R^(fc1) and R^(fc2) may bondtogether to form a ring with the linkage (—CF₂—SO₂—C⁻—SO₂—CF₂—) to whichthey are attached, and preferably the pair is a fluorinated ethylene orfluorinated propylene group.

In formula (1D), R^(fd) is a C₁-C₄₀ monovalent hydrocarbon group whichmay contain a heteroatom. The monovalent hydrocarbon group may bestraight, branched or cyclic and examples thereof are as exemplifiedabove for R¹⁷.

With respect to the synthesis of the sulfonium salt having an anion offormula (1D), reference is made to JP-A 2010-215608 and JP-A2014-133723.

Examples of the anion having formula (1D) are shown below, but notlimited thereto.

The compound having the anion of formula (1D) has a sufficient acidstrength to cleave acid labile groups in the base polymer because it isfree of fluorine at α-position of sulfo group, but has twotrifluoromethyl groups at β-position. Thus the compound is a useful PAG.

A compound having the formula (2) is also a useful PAG.

In formula (2), R²⁰¹ and R²⁰² are each independently a C₁-C₃₀ monovalenthydrocarbon group which may contain a heteroatom. R²⁰³ is a C₁-C₃₀divalent hydrocarbon group which may contain a heteroatom. Any two ofR²⁰¹, R²⁰² and R²⁰³ may bond together to form a ring with the sulfuratom to which they are attached. L^(A) is a single bond, ether bond or aC₁-C₂₀ divalent hydrocarbon group which may contain a heteroatom. X^(A),X^(B), X^(C) and X^(D) are each independently hydrogen, fluorine ortrifluoromethyl, with the proviso that at least one of X^(A), X^(B),X^(C) and X^(D) is fluorine or trifluoromethyl, and k is an integer of 0to 3.

The monovalent hydrocarbon group may be straight, branched or cyclic.Examples thereof include straight or branched alkyl groups such asmethyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl,n-pentyl, tert-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl, 2-ethylhexyl;monovalent saturated cyclic hydrocarbon groups such as cyclopentyl,cyclohexyl, cyclopentylmethyl, cyclopentylethyl, cyclopentylbutyl,cyclohexylmethyl, cyclohexylethyl, cyclohexylbutyl, norbornyl,oxanorbornyl, tricyclo[5.2.1.0^(2,6)]decanyl, adamantyl; aryl groupssuch as phenyl, naphthyl and anthracenyl. Also included are theforegoing groups in which some hydrogen is substituted by a moietycontaining a heteroatom such as oxygen, sulfur, nitrogen or halogen, orin which some carbon is replaced by a moiety containing a heteroatomsuch as oxygen, sulfur or nitrogen, so that the group may contain ahydroxyl, cyano, carbonyl, ether bond, ester bond, sulfonic acid esterbond, carbonate bond, lactone ring, sultone ring, carboxylic anhydrideor haloalkyl moiety.

The divalent hydrocarbon group may be straight, branched or cyclic.Examples thereof include straight or branched alkanediyl groups such asmethylene, ethylene, propane-1,3-diyl, butane-1,4-diyl,pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl,nonane-1,9-diyl, decane-1,10-diyl, undecane-1,11-diyl,dodecane-1,12-diyl, tridecane-1,13-diyl, tetradecane-1,14-diyl,pentadecane-1,15-diyl, hexadecane-1,16-diyl, heptadecane-1,17-diyl;divalent saturated cyclic hydrocarbon groups such as cyclopentanediyl,cyclohexanediyl, norbornanediyl, and adamantanediyl; and divalentunsaturated cyclic hydrocarbon groups such as phenylene and naphthylene.Also included are the foregoing groups in which some hydrogen issubstituted by an alkyl group such as methyl, ethyl, propyl, n-butyl ortert-butyl, or in which some hydrogen is substituted by a moietycontaining a heteroatom such as oxygen, sulfur, nitrogen or halogen, orin which some carbon is replaced by a moiety containing a heteroatomsuch as oxygen, sulfur or nitrogen, so that the group may contain ahydroxyl, cyano, carbonyl, ether bond, ester bond, sulfonic acid esterbond, carbonate, lactone ring, sultone ring, carboxylic anhydride orhaloalkyl moiety. The preferred heteroatom is oxygen.

Of the PAGs having formula (2), those having formula (2′) are preferred.

In formula (2′), L^(A) is as defined above. R is hydrogen ortrifluoromethyl, preferably trifluoromethyl. R³⁰¹, R³⁰² and R³⁰³ areeach independently hydrogen or a C₁-C₂₀ monovalent hydrocarbon groupwhich may contain a heteroatom. The monovalent hydrocarbon group may bestraight, branched or cyclic and examples thereof are as exemplifiedabove for R¹⁰⁷. The subscripts x and y each are an integer of 0 to 5,and z is an integer of 0 to 4.

Of the foregoing PAGs, those compounds having an anion of formula (1A′)or (1D) are especially preferred because of reduced acid diffusion andhigh solubility in resist solvent, and those compounds having an anionof formula (2′) are especially preferred because of minimized aciddiffusion.

Also sulfonium and iodonium salts having an anion containing an iodizedor brominated aromatic ring are useful PAGs. These salts typically havethe formulae (3-1) and (3-2).

In formulae (3-1) and (3-2), X is iodine or bromine. When s is at least2, groups X may be identical or different.

L¹ is a single bond, ether bond, ester bond, or a C₁-C₆ alkanediyl groupwhich may contain an ether bond or ester bond. The alkanediyl group maybe straight, branched or cyclic.

R⁴⁰¹ is hydroxyl, carboxyl, fluorine, chlorine, bromine, amino or aC₁-C₂₀ alkyl group, C₁-C₂₀ alkoxy group, C₂-C₁₀ alkoxycarbonyl, C₂-C₂₀acyloxy group, or C₁-C₂₀ alkylsulfonyloxy group, which may containfluorine, chlorine, bromine, hydroxyl, amino or C₁-C₁₀ alkoxy moiety, or—NR^(401A)—C(═O)—R^(401B) or —NR^(401A)—C(═O)—O—R^(401B). R^(401A) ishydrogen or a C₁-C₆ alkyl group which may contain halogen, hydroxyl,C₁-C₆ alkoxy, C₂-C₆ acyl or C₂-C₆ acyloxy moiety; R^(401B) is a C₁-C₆alkyl group, C₂-C₁₆ alkenyl group or C₆-C₁₂ aryl group, which maycontain halogen, hydroxyl, a C₁-C₆ alkoxy, C₂-C₆ acyl or C₂-C₆ acyloxymoiety. The alkyl, alkoxy, alkoxycarbonyl, acyloxy, acyl and alkenylgroups may be straight, branched or cyclic. When t is at least 2, groupsR⁴⁰¹ may be identical or different.

Inter alia, R⁴⁰¹ is preferably selected from hydroxyl,—NR^(401A)—C(═O)—R^(401B), —NR^(401A)—C(═O)—O—R^(401B), fluorine,chlorine, bromine, methyl, and methoxy.

R⁴⁰² is a single bond or a C₁-C₂₀ divalent linking group in case of r=1,and a C₁-C₂₀ tri- or tetravalent linking group in case of r=2 or 3. Thelinking group may contain oxygen, sulfur or nitrogen.

Rf¹ to Rf⁴ are each independently hydrogen, fluorine or trifluoromethyl,at least one thereof being fluorine or trifluoromethyl. Also Rf¹ andRf², taken together, may form a carbonyl group. Most preferably both Rf³and Rf⁴ are fluorine.

R⁴⁰³, R⁴⁰⁴, R⁴⁰⁵, R⁴⁰⁶ and R⁴⁰⁷ are each independently a C₁-C₂₀monovalent hydrocarbon group which may contain a heteroatom. Any two ofR⁴⁰³, R⁴⁰⁴ and R⁴⁰⁵ may bond together to form a ring with the sulfuratom to which they are attached. The monovalent hydrocarbon group may bestraight, branched or cyclic and examples thereof include C₁-C₁₂ alkylgroups, C₂-C₁₂ alkenyl groups, C₂-C₁₂ alkynyl groups, C₆-C₂₀ arylgroups, and C₇-C₁₂ aralkyl groups. In these groups, some or all hydrogenmay be substituted by hydroxyl, carboxyl, halogen, cyano, nitro,mercapto, sultone, sulfone, or sulfonium salt-containing moiety; or somecarbon may be replaced by an ether bond, ester bond, carbonyl, amidebond, carbonate or sulfonic acid ester bond.

The subscript r is an integer of 1 to 3. The subscript s is an integerof 1 to 5, and t is an integer of 0 to 3, meeting 1≤s+t≤5. Preferably, sis an integer of 1 to 3, more preferably 2 or 3, and t is an integer of0 to 2.

The cation moiety in the sulfonium salt having formula (3-1) is asexemplified above for the cation moiety in the sulfonium salt havingformula (Aa). The cation moiety in the iodonium salt having formula(3-2) is as exemplified above for the cation moiety in the iodonium salthaving formula (1-2).

The acid generator of addition type may be used alone or in admixture.When used, the acid generator is preferably added in an amount of 0.1 to200 parts, more preferably 1 to 100 parts by weight per 100 parts byweight of the base polymer.

Other Components

With the foregoing components, other components such as an organicsolvent, surfactant, dissolution inhibitor, and crosslinker may beblended in any desired combination to formulate a positive or negativeresist composition. This positive or negative resist composition has avery high sensitivity in that the dissolution rate in developer of thebase polymer in exposed areas is accelerated by catalytic reaction. Inaddition, the resist film has a high dissolution contrast, resolution,exposure latitude, and process adaptability, and provides a good patternprofile after exposure, and minimal proximity bias because of restrainedacid diffusion. By virtue of these advantages, the composition is fullyuseful in commercial application and suited as a pattern-formingmaterial for the fabrication of VLSIs. Particularly when an acidgenerator is incorporated to formulate a chemically amplified positiveresist composition capable of utilizing acid catalyzed reaction, thecomposition has a higher sensitivity and is further improved in theproperties described above.

Examples of the organic solvent used herein are described in JP-A2008-111103, paragraphs [0144]-[0145] (U.S. Pat. No. 7,537,880).Exemplary solvents include ketones such as cyclohexanone, cyclopentanoneand methyl-2-n-pentyl ketone; alcohols such as 3-methoxybutanol,3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol,and diacetone alcohol (DAA); ethers such as propylene glycol monomethylether, ethylene glycol monomethyl ether, propylene glycol monoethylether, ethylene glycol monoethyl ether, propylene glycol dimethyl ether,and diethylene glycol dimethyl ether; esters such as propylene glycolmonomethyl ether acetate (PGMEA), propylene glycol monoethyl etheracetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl3-methoxypropionate, ethyl 3-ethoxypropionate, t-butyl acetate, t-butylpropionate, and propylene glycol mono-t-butyl ether acetate; andlactones such as γ-butyrolactone, which may be used alone or inadmixture.

The organic solvent is preferably added in an amount of 100 to 10,000parts, and more preferably 200 to 8,000 parts by weight per 100 parts byweight of the base polymer.

Exemplary surfactants are described in JP-A 2008-111103, paragraphs[0165]-[0166].

Inclusion of a surfactant may improve or control the coatingcharacteristics of the resist composition. The surfactant may be usedalone or in admixture. The surfactant is preferably added in an amountof 0.0001 to 10 parts by weight per 100 parts by weight of the basepolymer.

In the case of a positive resist composition, inclusion of a dissolutioninhibitor may lead to an increased difference in dissolution ratebetween exposed and unexposed areas and a further improvement inresolution. The dissolution inhibitor which can be used herein is acompound having at least two phenolic hydroxyl groups on the molecule,in which an average of from 0 to 100 mol % of all the hydrogen atoms onthe phenolic hydroxyl groups are replaced by acid labile groups or acompound having at least one carboxyl group on the molecule, in which anaverage of 50 to 100 mol % of all the hydrogen atoms on the carboxylgroups are replaced by acid labile groups, both the compounds having amolecular weight of 100 to 1,000, and preferably 150 to 800. Typical arebisphenol A, trisphenol, phenolphthalein, cresol novolac,naphthalenecarboxylic acid, adamantanecarboxylic acid, and cholic acidderivatives in which the hydrogen atom on the hydroxyl or carboxyl groupis replaced by an acid labile group, as described in U.S. Pat. No.7,771,914 (JP-A 2008-122932, paragraphs [0155]-[0178]).

In the resist composition which is positive, the dissolution inhibitoris preferably added in an amount of 0 to 50 parts, more preferably 5 to40 parts by weight per 100 parts by weight of the base polymer. Thedissolution inhibitor may be used alone or in admixture.

In the case of a negative resist composition, a crosslinker is addedthereto to reduce the dissolution rate in the exposed region of a resistfilm, yielding a negative pattern. Suitable crosslinkers which can beused herein include epoxy compounds, melamine compounds, guanaminecompounds, glycoluril compounds and urea compounds having substitutedthereon at least one group selected from among methylol, alkoxymethyland acyloxymethyl groups, isocyanate compounds, azide compounds, andcompounds having a double bond such as an alkenyl ether group. Thesecompounds may be used as an additive or introduced into a polymer sidechain as a pendant. Hydroxy-containing compounds may also be used as thecrosslinker. The crosslinker may be used alone or in admixture.

Of the foregoing crosslinkers, suitable epoxy compounds includetris(2,3-epoxypropyl) isocyanurate, trimethylolmethane triglycidylether, trimethylolpropane triglycidyl ether, and triethylolethanetriglycidyl ether. Examples of the melamine compound includehexamethylol melamine, hexamethoxymethyl melamine, hexamethylol melaminecompounds having 1 to 6 methylol groups methoxymethylated and mixturesthereof, hexamethoxyethyl melamine, hexaacyloxymethyl melamine,hexamethylol melamine compounds having 1 to 6 methylol groupsacyloxymethylated and mixtures thereof. Examples of the guanaminecompound include tetramethylol guanamine, tetramethoxymethyl guanamine,tetramethylol guanamine compounds having 1 to 4 methylol groupsmethoxymethylated and mixtures thereof, tetramethoxyethyl guanamine,tetraacyloxyguanamine, tetramethylol guanamine compounds having 1 to 4methylol groups acyloxymethylated and mixtures thereof. Examples of theglycoluril compound include tetramethylol glycoluril,tetramethoxyglycoluril, tetramethoxymethyl glycoluril, tetramethylolglycoluril compounds having 1 to 4 methylol groups methoxymethylated andmixtures thereof, tetramethylol glycoluril compounds having 1 to 4methylol groups acyloxymethylated and mixtures thereof. Examples of theurea compound include tetramethylol urea, tetramethoxymethyl urea,tetramethylol urea compounds having 1 to 4 methylol groupsmethoxymethylated and mixtures thereof, and tetramethoxyethyl urea.

Suitable isocyanate compounds include tolylene diisocyanate,diphenylmethane diisocyanate, hexamethylene diisocyanate and cyclohexanediisocyanate. Suitable azide compounds include1,1′-biphenyl-4,4′-bisazide, 4,4′-methylidenebisazide, and4,4′-oxybisazide. Examples of the alkenyl ether group-containingcompound include ethylene glycol divinyl ether, triethylene glycoldivinyl ether, 1,2-propanediol divinyl ether, 1,4-butanediol divinylether, tetramethylene glycol divinyl ether, neopentyl glycol divinylether, trimethylol propane trivinyl ether, hexanediol divinyl ether,1,4-cyclohexanediol divinyl ether, pentaerythritol trivinyl ether,pentaerythritol tetravinyl ether, sorbitol tetravinyl ether, sorbitolpentavinyl ether, and trimethylol propane trivinyl ether.

In the negative resist composition, the crosslinker is preferably addedin an amount of 0.1 to 50 parts, more preferably 1 to 40 parts by weightper 100 parts by weight of the base polymer.

In the resist composition of the invention, a quencher of the structurenot containing an iodized benzene ring (referred to as another quencher)may be blended. The other quencher is typically selected fromconventional basic compounds. Conventional basic compounds includeprimary, secondary, and tertiary aliphatic amines, mixed amines,aromatic amines, heterocyclic amines, nitrogen-containing compounds withcarboxyl group, nitrogen-containing compounds with sulfonyl group,nitrogen-containing compounds with hydroxyl group, nitrogen-containingcompounds with hydroxyphenyl group, alcoholic nitrogen-containingcompounds, amide derivatives, imide derivatives, and carbamatederivatives. Also included are primary, secondary, and tertiary aminecompounds, specifically amine compounds having a hydroxyl, ether, ester,lactone ring, cyano, or sulfonic acid ester group as described in JP-A2008-111103, paragraphs [0146]-[0164], and compounds having a carbamategroup as described in JP 3790649. Addition of a basic compound may beeffective for further suppressing the diffusion rate of acid in theresist film or correcting the pattern profile.

Onium salts such as sulfonium salts, iodonium salts and ammonium saltsof sulfonic acids which are not fluorinated at α-position as describedin U.S. Pat. No. 8,795,942 (JP-A 2008-158339) and similar onium salts ofcarboxylic acid may also be used as the other quencher. While anα-fluorinated sulfonic acid, imide acid, and methide acid are necessaryto deprotect the acid labile group of carboxylic acid ester, anα-non-fluorinated sulfonic acid or carboxylic acid is released by saltexchange with an α-non-fluorinated onium salt. An α-non-fluorinatedsulfonic acid and a carboxylic acid function as a quencher because theydo not induce deprotection reaction.

To the resist composition, a water repellency improver may also be addedfor improving the water repellency on surface of a resist film as spincoated. The water repellency improver may be used in the topcoatlessimmersion lithography. Suitable water repellency improvers includepolymers having a fluoroalkyl group and polymers having a specificstructure with a 1,1,1,3,3,3-hexafluoro-2-propanol residue and aredescribed in JP-A 2007-297590 and JP-A 2008-111103, for example. Thewater repellency improver to be added to the resist composition shouldbe soluble in the organic solvent as the developer. The water repellencyimprover of specific structure with a 1,1,1,3,3,3-hexafluoro-2-propanolresidue is well soluble in the developer. A polymer having an aminogroup or amine salt copolymerized as recurring units may serve as thewater repellent additive and is effective for preventing evaporation ofacid during PEB, thus preventing any hole pattern opening failure afterdevelopment. The water repellency improver may be used alone or inadmixture. An appropriate amount of the water repellency improver is 0to 20 parts, preferably 0.5 to 10 parts by weight per 100 parts byweight of the base polymer.

Also, an acetylene alcohol may be blended in the resist composition.Suitable acetylene alcohols are described in JP-A 2008-122932,paragraphs [0179]-[0182]. An appropriate amount of the acetylene alcoholblended is 0 to 5 parts by weight per 100 parts by weight of the basepolymer.

Pattern Forming Process

The resist composition is used in the fabrication of various integratedcircuits. Pattern formation using the resist composition may beperformed by well-known lithography processes. The process generallyinvolves coating, exposure, and development. If necessary, anyadditional steps may be added.

For example, the positive resist composition is first applied onto asubstrate on which an integrated circuit is to be formed (e.g., Si,SiO₂, SiN, SiON, TiN, WSi, BPSG, SOG, or organic antireflective coating)or a substrate on which a mask circuit is to be formed (e.g., Cr, CrO,CrON, MoSi₂, or SiO₂) by a suitable coating technique such as spincoating, roll coating, flow coating, dipping, spraying or doctorcoating. The coating is prebaked on a hotplate at a temperature of 60 to150° C. for 10 seconds to 30 minutes, preferably at 80 to 120° C. for 30seconds to 20 minutes. The resulting resist film is generally 0.01 to2.0 μm thick.

The resist film is then exposed to a desired pattern of high-energyradiation such as UV, deep-UV, EB, EUV of wavelength 3 to 15 nm, x-ray,soft x-ray, excimer laser light, γ-ray or synchrotron radiation. WhenUV, deep-UV, EUV, x-ray, soft x-ray, excimer laser, γ-ray or synchrotronradiation is used as the high-energy radiation, the resist film isexposed thereto through a mask having a desired pattern in a dose ofpreferably about 1 to 200 mJ/cm², more preferably about 10 to 100mJ/cm². When EB is used as the high-energy radiation, the resist film isexposed thereto through a mask having a desired pattern or directly in adose of preferably about 0.1 to 100 μC/cm², more preferably about 0.5 to50 μC/cm². It is appreciated that the inventive resist composition issuited in micropatterning using KrF excimer laser, ArF excimer laser,EB, EUV, x-ray, soft x-ray, γ-ray or synchrotron radiation, especiallyin micropatterning using EB or EUV.

After the exposure, the resist film may be baked (PEB) on a hot plate at60 to 150° C. for 10 seconds to 30 minutes, preferably at 80 to 120° C.for 30 seconds to 20 minutes.

After the exposure or PEB, the resist film is developed in a developerin the form of an aqueous base solution for 3 seconds to 3 minutes,preferably 5 seconds to 2 minutes by conventional techniques such asdip, puddle and spray techniques. A typical developer is a 0.1 to 10 wt%, preferably 2 to 5 wt % aqueous solution of tetramethylammoniumhydroxide (TMAH), tetraethylammonium hydroxide (TEAH),tetrapropylammonium hydroxide (TPAH), or tetrabutylammonium hydroxide(TBAH). The resist film in the exposed area is dissolved in thedeveloper whereas the resist film in the unexposed area is notdissolved. In this way, the desired positive pattern is formed on thesubstrate. Inversely in the case of negative resist, the exposed area ofresist film is insolubilized and the unexposed area is dissolved in thedeveloper.

In an alternative embodiment, a negative pattern may be formed viaorganic solvent development using a positive resist compositioncomprising a base polymer having an acid labile group. The developerused herein is preferably selected from among 2-octanone, 2-nonanone,2-heptanone, 3-heptanone, 4-heptanone, 2-hexanone, 3-hexanone,diisobutyl ketone, methylcyclohexanone, acetophenone,methylacetophenone, propyl acetate, butyl acetate, isobutyl acetate,pentyl acetate, butenyl acetate, isopentyl acetate, propyl formate,butyl formate, isobutyl formate, pentyl formate, isopentyl formate,methyl valerate, methyl pentenoate, methyl crotonate, ethyl crotonate,methyl propionate, ethyl propionate, ethyl 3-ethoxypropionate, methyllactate, ethyl lactate, propyl lactate, butyl lactate, isobutyl lactate,pentyl lactate, isopentyl lactate, methyl 2-hydroxyisobutyrate, ethyl2-hydroxyisobutyrate, methyl benzoate, ethyl benzoate, phenyl acetate,benzyl acetate, methyl phenylacetate, benzyl formate, phenylethylformate, methyl 3-phenylpropionate, benzyl propionate, ethylphenylacetate, and 2-phenylethyl acetate, and mixtures thereof.

At the end of development, the resist film is rinsed. As the rinsingliquid, a solvent which is miscible with the developer and does notdissolve the resist film is preferred. Suitable solvents includealcohols of 3 to 10 carbon atoms, ether compounds of 8 to 12 carbonatoms, alkanes, alkenes, and alkynes of 6 to 12 carbon atoms, andaromatic solvents. Specifically, suitable alcohols of 3 to 10 carbonatoms include n-propyl alcohol, isopropyl alcohol, 1-butyl alcohol,2-butyl alcohol, isobutyl alcohol, t-butyl alcohol, 1-pentanol,2-pentanol, 3-pentanol, t-pentyl alcohol, neopentyl alcohol,2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol,cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol,3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-ethyl-1-butanol,2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol,3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol,4-methyl-1-pentanol, 4-methyl-2-pentanol, 4-methyl-3-pentanol,cyclohexanol, and 1-octanol. Suitable ether compounds of 8 to 12 carbonatoms include di-n-butyl ether, diisobutyl ether, di-s-butyl ether,di-n-pentyl ether, diisopentyl ether, di-s-pentyl ether, di-t-pentylether, and di-n-hexyl ether. Suitable alkanes of 6 to 12 carbon atomsinclude hexane, heptane, octane, nonane, decane, undecane, dodecane,methylcyclopentane, dimethylcyclopentane, cyclohexane,methylcyclohexane, dimethylcyclohexane, cycloheptane, cyclooctane, andcyclononane. Suitable alkenes of 6 to 12 carbon atoms include hexene,heptene, octene, cyclohexene, methylcyclohexene, dimethylcyclohexene,cycloheptene, and cyclooctene. Suitable alkynes of 6 to 12 carbon atomsinclude hexyne, heptyne, and octyne. Suitable aromatic solvents includetoluene, xylene, ethylbenzene, isopropylbenzene, t-butylbenzene andmesitylene.

Rinsing is effective for minimizing the risks of resist pattern collapseand defect formation. However, rinsing is not essential. If rinsing isomitted, the amount of solvent used may be reduced.

A hole or trench pattern after development may be shrunk by the thermalflow, RELACS® or DSA process. A hole pattern is shrunk by coating ashrink agent thereto, and baking such that the shrink agent may undergocrosslinking at the resist surface as a result of the acid catalystdiffusing from the resist layer during bake, and the shrink agent mayattach to the sidewall of the hole pattern. The bake is preferably at atemperature of 70 to 180° C., more preferably 80 to 170° C., for a timeof 10 to 300 seconds. The extra shrink agent is stripped and the holepattern is shrunk.

EXAMPLES

Examples of the invention are given below by way of illustration and notby way of limitation. All parts are by weight (pbw).

Quenchers 1 to 14 used in resist compositions have the structure shownbelow. A sulfonium salt was synthesized by ion exchange with a sulfoniumchloride providing the cation shown below. A quaternary ammonium saltwas synthesized by ion exchange with a quaternary ammonium chloride. Atertiary ammonium compound was synthesized by mixing a tertiary aminecompound with a carboxyl-containing compound.

Synthesis Example Synthesis of base polymers (Polymers 1 to 12,Comparative Polymers 1, 2)

Base polymers were prepared by combining suitable monomers, effectingcopolymerization reaction thereof in tetrahydrofuran (THF) solvent,pouring the reaction solution into methanol for crystallization,repeatedly washing with hexane, isolation, and drying. The resultingpolymers, designated Polymers 1 to 12 and Comparative Polymers 1 and 2,were analyzed for composition by ¹H-NMR spectroscopy, and for Mw andMw/Mn by GPC versus polystyrene standards using THF solvent.

Examples 1 to 25 and Comparative Examples 1 to 10

[1] Preparation of Resist Composition

Resist compositions were prepared by dissolving the selected componentsin a solvent in accordance with the recipe shown in Tables 1 and 2, andfiltering through a filter having a pore size of 0.2 μm. The solventcontained 100 ppm of surfactant FC-4430 (3M). The components in Tables 1and 2 are as identified below.

Organic Solvents:

-   -   PGMEA (propylene glycol monomethyl ether acetate)    -   DAA (diacetone alcohol)        Acid generator: PAG 1 to PAG 6 of the following structural        formulae

Comparative quenchers 1 to 7 of the following structural formulae

[2] EUV Lithography Test

Each of the resist compositions in Tables 1 and 2 was spin coated on asilicon substrate having a 20-nm coating of silicon-containing spin-onhard mask SHB-A940 (Shin-Etsu Chemical Co., Ltd., Si content 43 wt %)and prebaked on a hotplate at 105° C. for 60 seconds to form a resistfilm of 50 nm thick. Using an EUV scanner NXE3300 (ASML, NA 0.33, σ0.9/0.6, quadrupole illumination), the resist film was exposed to EUVthrough a mask bearing a hole pattern at a pitch 46 nm (on-wafer size)and +20% bias. The resist film was baked (PEB) on a hotplate at thetemperature shown in Tables 1 and 2 for 60 seconds and developed in a2.38 wt % TMAH aqueous solution for 30 seconds to form a pattern. InExamples 1 to 20 and Comparative Examples 1 to 9, a positive resistpattern, i.e., hole pattern having a size of 23 nm was formed. InExample 21 and Comparative Example 10, a negative resist pattern, i.e.,dot pattern having a size of 23 nm was formed.

The resist pattern was observed under CD-SEM (CG-5000, HitachiHigh-Technologies Corp.). The exposure dose that provides a hole or dotpattern having a size of 23 nm is reported as sensitivity. The size of50 holes or dots was measured, from which a size variation (3a) wascomputed and reported as CDU.

The resist composition is shown in Tables 1 and 2 together with thesensitivity and CDU of EUV lithography.

TABLE 1 Acid Organic PEB Polymer generator Quencher solvent temp.Sensitivity CDU (pbw) (pbw) (pbw) (pbw) (° C.) (mJ/cm²) (nm) Example 1Polymer 1 PAG 1 Quencher 1 PGMEA (2,000) 95 27 3.6 (100) (20.0) (5.10)DAA (500) 2 Polymer 1 PAG 1 Quencher 2 PGMEA (2,000) 95 25 3.0 (100)(20.0) (6.51) DAA (500) 3 Polymer 1 PAG 1 Quencher 3 PGMEA (2,000) 95 243.3 (100) (20.0) (7.61) DAA (500) 4 Polymer 1 PAG 1 Quencher 4 PGMEA(2,000) 95 26 3.2 (100) (20.0) (3.00) DAA (500) 5 Polymer 1 PAG 1Quencher 5 PGMEA (2,000) 95 25 3.3 (100) (20.0) (10.63) DAA (500) 6Polymer 1 PAG 1 Quencher 6 PGMEA (2,000) 95 26 3.1 (100) (20.0) (7.41)DAA (500) 7 Polymer 1 PAG 2 Quencher 7 PGMEA (2,000) 95 26 3.0 (100)(22.0) (8.28) DAA (500) 8 Polymer 1 PAG 3 Quencher 8 PGMEA (2,000) 95 243.0 (100) (20.0) (8.38) DAA (500) 9 Polymer 1 PAG 4 Quencher 9 PGMEA(2,000) 95 26 3.0 (100) (26.0) (6.61) DAA (500) 10 Polymer 1 PAG 5Quencher 10 PGMEA (2,000) 95 26 3.1 (100) (24.0) (6.12) DAA (500) 11Polymer 1 PAG 6 Quencher 11 PGMEA (2,000) 95 27 3.2 (100) (24.0) (6.10)DAA (500) 12 Polymer 1 PAG 1 Quencher 12 PGMEA (2,000) 95 28 3.0 (100)(20.0) (6.52) DAA (500) 13 Polymer 1 PAG 1 Quencher 13 PGMEA (2,000) 9524 2.8 (100) (20.0) (10.00)  DAA (500) 14 Polymer 1 PAG 1 Quencher 14PGMEA (2,000) 95 25 2.9 (100) (20.0) (8.24) DAA (500) 15 Polymer 3 —Quencher 2 PGMEA (2,000) 95 24 2.7 (100) (6.51) DAA (500) 16 Polymer 4 —Quencher 2 PGMEA (2,000) 95 24 2.6 (100) (6.51) DAA (500) 17 Polymer 5 —Quencher 2 PGMEA (2,000) 95 24 2.7 (100) (6.51) DAA (500) 18 Polymer 6 —Quencher 2 PGMEA (2,000) 95 26 2.7 (100) (6.51) DAA (500) 19 Polymer 7 —Quencher 2 PGMEA (2,000) 95 25 2.6 (100) (6.51) DAA (500) 20 Polymer 8 —Quencher 2 PGMEA (2,000) 95 26 2.8 (100) (6.51) DAA (500) 21 Polymer 2PAG 1 Quencher 2 PGMEA (2,000) 95 35 3.7 (100) (15.0) (3.00) DAA (500)22 Polymer 9 — Quencher 2 PGMEA (2,000) 95 28 2.6 (100) (6.51) DAA (500)23 Polymer 10 — Quencher 2 PGMEA (2,000) 95 27 2.7 (100) (6.51) DAA(500) 24 Polymer 11 — Quencher 2 PGMEA (2,000) 95 26 2.6 (100) (6.51)DAA (500) 25 Polymer 12 — Quencher 2 PGMEA (2,000) 95 24 2.6 (100)(6.51) DAA (500)

Acid PEB Polymer generator Quencher Organic solvent temp. SensitivityCDU (pbw) (pbw) (pbw) (pbw) (° C.) (mJ/cm²) (nm) Comparative 1 Polymer 1PAG 1 Comparative PGMEA (2,000) 95 29 3.8 Example (100) (20.0) quencher1 DAA (500) (4.72) 2 Polymer 1 PAG 1 Comparative PGMEA (2,000) 95 30 3.9(100) (20.0) quencher 2 DAA (500) (6.04) 3 Polymer 1 PAG 1 ComparativePGMEA (2,000) 95 32 3.8 (100) (20.0) quencher 3 DAA (500) (4.00) 4Polymer 1 PAG 1 Comparative PGMEA (2,000) 95 31 3.7 (100) (20.0)quencher 4 DAA (500) (4.36) 5 Polymer 1 PAG 1 Comparative PGMEA (2,000)95 36 4.1 (100) (20.0) quencher 5 DAA (500) (2.94) 6 Polymer 1 PAG 1Comparative PGMEA (2,000) 95 38 4.0 (100) (20.0) quencher 6 DAA (500)(4.53) 7 Polymer 1 PAG 1 Comparative PGMEA (2,000) 95 37 3.9 (100)(20.0) quencher 7 DAA (500) (3.63) 8 Comparative PAG 1 Quencher 1 PGMEA(2,000) 95 35 3.9 Polymer 1 (20.0) (5.10) DAA (500) (100) 9 ComparativePAG 1 Comparative PGMEA (2,000) 95 39 4.1 Polymer 1 (20.0) quencher 1DAA (500) (100) (4.72) 10 Comparative PAG 1 Quencher 1 PGMEA (2,000) 9545 4.5 Polymer 2 (15.0) (5.10) DAA (500) (100)

It is demonstrated in Tables 1 and 2 that resist compositions comprisingan iodized polymer and an iodized benzene ring-containing quencherwithin the scope of the invention offer a high sensitivity and improvedCDU.

Japanese Patent Application No. 2018-236571 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

The invention claimed is:
 1. A resist composition comprising an iodizedbase polymer, and at least one quencher selected from the groupconsisting of a sulfonium or ammonium salt of iodized benzenering-containing carboxylic acid, a sulfonium or ammonium salt of iodizedbenzene ring-containing N-carbonylsulfonamide, and an iodized benzenering-containing ammonium salt, wherein the sulfonium or ammonium salt ofiodized benzene ring-containing carboxylic acid, the sulfonium orammonium salt of iodized benzene ring-containing N-carbonylsulfonamide,and the iodized benzene ring-containing ammonium salt have the followingformulae (A)-1, (A)-2 and (A)-4, respectively,

wherein R¹ is hydroxyl, fluorine, chlorine, bromine, amino, nitro,cyano, or a C₁-C₆ alkyl group, C₁-C₆ alkoxy group, C₂-C₆ acyloxy groupor C₁-C₄ alkylsulfonyloxy group, which may be substituted with halogen,or —NR^(1A)—C(═O)—R^(1B) or —NR^(1A)—C(═O)—O—R^(1B), R^(1A) is hydrogenor a C₁-C₆ alkyl group, R^(1B) is a C₁-C₆ alkyl group or C₂-C₈ alkenylgroup, R² is a single bond or a C₁-C₂₀ divalent linking group which maycontain ether bond, carbonyl moiety, ester bond, amide bond, sultonemoiety, lactam moiety, carbonate moiety, halogen, hydroxyl moiety orcarboxyl moiety, R³ is a C₁-C₁₀ alkyl group or C₆-C₁₀ aryl group, whichmay be substituted with amino, nitro, cyano, C₁-C₁₂ alkyl, C₁-C₁₂alkoxy, C₂-C₁₂ alkoxycarbonyl, C₂-C₁₂ acyl, C₂-C₁₂ acyloxy, hydroxyl orhalogen, R⁴ is a C₁-C₂₀ divalent hydrocarbon group which may contain anester bond or ether bond, R⁵ is hydrogen, nitro, or a C₁-C₂₀ monovalenthydrocarbon group which may contain hydroxyl, carboxyl, ether bond,ester bond, thiol, nitro, cyano or amino, with the proviso that in caseof p=1, groups R⁵ may bond together to form a ring with the nitrogenatom to which they are attached, the ring optionally containing a doublebond, oxygen, sulfur or nitrogen, m is an integer of 1 to 5, n is aninteger of 0 to 4, meeting 1≤m+n≤5, p is 1, 2 or 3, q is 1 or 2, A^(q−)is a carboxylate anion, fluorine-free sulfonimide anion, sulfonamideanion, or halide ion, X⁺ is a sulfonium cation having the formula (Aa)or ammonium cation having the formula (Ab):

wherein R⁶, R⁷ and R⁸ are each independently fluorine, chlorine,bromine, iodine, or a C₁-C₂₀ monovalent hydrocarbon group which maycontain a heteroatom, R⁶ and R⁷ may bond together to form a ring withthe sulfur atom to which they are attached, R⁹ to R¹² are eachindependently hydrogen or a C₁-C₂₄ monovalent hydrocarbon group whichmay contain halogen, hydroxyl, carboxyl, thiol, ether bond, ester bond,thioester bond, thionoester bond, dithioester bond, amino, nitro,sulfone or ferrocenyl, R⁹ and R¹⁰ may bond together to form a ring, R⁹and R¹⁰ taken together may form ═C(R^(9A))(R^(10A)), R^(9A) and R^(10A)are each independently hydrogen or a C₁-C₁₆ monovalent hydrocarbongroup, R^(9A) and R^(10A) may bond together to form a ring with thecarbon and nitrogen atoms to which they are attached, the ringoptionally containing a double bond, oxygen, sulfur or nitrogen, whereinthe iodized base polymer comprises recurring units having the formula(a1) or recurring units having the formula (a2):

wherein R^(A) is each independently hydrogen or methyl, R²¹ is a singlebond or methylene, R²² is hydrogen or a C₁-C₄ alkyl group, X¹ is asingle bond, ether bond, ester bond, amide bond, —C(═O)—O—R²³—,phenylene, -Ph-C(═O)—O—R²⁴—, or -Ph-R²⁵—O—C(═O)—R²⁶—, wherein Ph standsfor phenyl, R²³ is a C₁-C₁₀ alkanediyl group which may contain an etherbond or ester bond, R²⁴, R²⁵ and R²⁶ are each independently a singlebond or a C₁-C₆ straight or branched alkanediyl group, a is an integerof 1 to 5, b is an integer of 1 to 4, meeting 1≤a+b≤5.
 2. The resistcomposition of claim 1, further comprising an acid generator capable ofgenerating sulfonic acid, imidic acid or methide acid.
 3. The resistcomposition of claim 1 wherein a is an integer of 1 to
 3. 4. The resistcomposition of claim 1, further comprising an organic solvent.
 5. Theresist composition of claim 1 wherein the iodized base polymer furthercomprises recurring units having the formula (b1) or recurring unitshaving the formula (b2):

wherein R^(A) is each independently hydrogen or methyl, Y¹ is a singlebond, phenylene, naphthylene, or a C₁-C₁₂ linking group containing anester bond or lactone ring, Y² is a single bond or ester bond, R³¹ andR³² are each independently an acid labile group, R³³ is fluorine,trifluoromethyl, cyano, a C₁-C₆ alkyl, C₁-C₆ alkoxy, C₂-C₇ acyl, C₂-C₇acyloxy, or C₂-C₇ alkoxycarbonyl group, R³⁴ is a single bond or C₁-C₆alkanediyl group in which some carbon may be replaced by an ether orester bond, c is 1 or 2, d is an integer of 0 to 4, meeting 1≤c+d≤5. 6.The resist composition of claim 5, further comprising a dissolutioninhibitor.
 7. The resist composition of claim 5 which is a chemicallyamplified positive resist composition.
 8. The resist composition ofclaim 1 wherein the iodized base polymer is free of an acid labilegroup.
 9. The resist composition of claim 8, further comprising acrosslinker.
 10. The resist composition of claim 8 which is a chemicallyamplified negative resist composition.
 11. The resist composition ofclaim 1, further comprising an iodine-free quencher.
 12. The resistcomposition of claim 1, further comprising a surfactant.
 13. The resistcomposition of claim 1 wherein the iodized base polymer furthercomprises recurring units of at least one type selected from recurringunits having the formulae (g1) to (g3):

wherein R^(A) is each independently hydrogen or methyl, Z¹ is a singlebond, phenylene, —O—Z¹²—, —C(═O)—Z¹¹—Z¹²—, Z¹¹ is —O— or —NH—, Z¹² is aC₁-C₆ alkanediyl group, C₂-C₆ alkenediyl group or phenylene group, whichmay contain a carbonyl moiety, ester bond, ether bond or hydroxylmoiety, Z² is a single bond, —Z²¹—C(═O)—O—, —Z²¹—O—, or —Z²¹—O—C(═O)—,Z²¹ is a C₁-C₁₂ alkanediyl group which may contain a carbonyl moiety,ester bond or ether bond, Z³ is a single bond, methylene, ethylene,phenylene, fluorinated phenylene, —O—Z³²—, or —C(═O)—Z³¹—Z³²—, Z³¹ is—O— or —NH—, Z³² is a C₁-C₆ alkanediyl group, phenylene, fluorinatedphenylene, trifluoromethyl-substituted phenylene group, or C₂-C₆alkenediyl group, which may contain a carbonyl moiety, ester bond, etherbond or hydroxyl moiety, R⁴¹ to R⁴⁸ are each independently a C₁-C₂₀monovalent hydrocarbon group which may contain a heteroatom, any two ofR⁴³, R⁴⁴ and R⁴⁵ or any two of R⁴⁶, R⁴⁷ and R⁴⁸ may bond together toform a ring with the sulfur atom to which they are attached, A ishydrogen or trifluoromethyl, and Q⁻ is a non-nucleophilic counter ion.14. A pattern forming process comprising the steps of applying theresist composition of claim 1 to form a resist film on a substrate,exposing the resist film to high-energy radiation, and developing theexposed resist film in a developer.
 15. The process of claim 14 whereinthe high-energy radiation is ArF excimer laser of wavelength 193 nm orKrF excimer laser of wavelength 248 nm.
 16. The process of claim 14wherein the high-energy radiation is EB or EUV of wavelength 3 to 15 nm.17. The resist composition of claim 1 wherein the quencher is selectedfrom the group consisting of a sulfonium or ammonium salt of iodizedbenzene ring-containing N-carbonylsulfonamide having the formula (A)-2,and an iodized benzene ring-containing ammonium salt having the formula(A)-4.